If a makefile "include"s another makefile that doesn't exist and which make doesn't know how to create, make fails. This is normally correct.

However, say there are two "include"d files, both of which are generated. Say make knows how to build the first one, and the contents of the first one will include instructions on how to build the second one.

In this case, make still fails although it could succeed, by building the first file, then re-execing itself, whereupon it would know how to build the second one.